The Significance And Zicon U-Pb Chronology Of Felsic Dykes In Taihe Panxi Area

The Taihe layered gabbroic intrusion that host giant Fe–Ti oxide deposit located in the central part of the Emeishan Large Igneous Province(ELIP), SW China. The most intensively studied ELIP documented the Taihe intrusion was formed at 260 Ma, together with the other layered intrusions in the central ELIP due to the mantle plume activity. Statistics suggest that the zircon U-Pb ages of the flood basalts and the Taihe layered gabbroic intrusion yield a quite wide range of 250-280 Ma. There’s some discrepancy between statistics and concordant age of the zircons. In this study, we choose the zircon U-Pb ages of the Taihe felsic dykes as a breakthrough. Carrying out geochemical data,U-Pb dating, Hf isotope analysis on zircons from the Taihe felsic dykes and using the MELTs to simulate the evolution of magma. Providing evidence for the wide range of the zircon age. Monzonlite, adamellite, monzonitic granite and granite have been confirmed by the petrography and geochemical analysis. Most of the zircons in the felsic dykes is formed by the crystallization of mafic magma. All of the analyses show Th/U ratios within the range exhibited by the zircons from the mafic magma.The Taihe felsic dykes province yield U–Pb dates at 269.9±2.7Ma, the ages of zircon can be roughly divided into three different groups(260Ma, 270 Ma, 280Ma). Zircon from these rocks exhibits a wide range of initial Hf isotope ratios(εHf(t) = +4.50 to +12.38), with corresponding TDM1 of 400–750 Ma, suggesting that their source is primarily juvenile crust added during Emeishan volcanism. Three types of parent magma have been selected, Using the MELTs to simulate crystallization differentiation and partial melting.the Taihe felsic dykes, are hybrid products of partial melting of deep mafic magma, crystallization differentiation of feldspar in the middle magma chamber and injecting into the acidic magma in the shallow magma chamber.Based on research above, mafic magma have been intruded into the lithospheric mantle or crust near the Moho before large-scale magmatic activity.